Post-void residual (PVR) refers to the volume of urine that remains in the urinary bladder immediately after a person has finished urinating. It is measured using ultrasound, either with a dedicated bladder scanner or a standard ultrasound machine, by calculating the bladder volume based on three dimensions (length, width, and depth) multiplied by a correction factor. A normal post-void residual is generally less than 50 milliliters, while values above 100 to 200 milliliters may suggest bladder outlet obstruction (commonly from an enlarged prostate), neurogenic bladder, or detrusor muscle weakness. PVR measurement is a simple, non-invasive test that provides clinically important information about urinary function and is commonly performed in urology, primary care, and hospital settings.